Telecommunication cables, whether of the metallic or fiber optic variety, are frequently employed in situations wherein water can enter and migrate through the cable system. Water entry into either copper or fiber optic cables is undesirable because it leads to deterioration of transmission properties due to corrosion, particularly at the sites where cables are spliced together. In order to protect the cable system, it has become known to encase certain segments of the cable in a closure which acts as an extension of the cable sheath or cover. In addition, it has become known to encapsulate the enclosed segment with a curable encapsulant so as to prevent water migration into the segment.
Examples of cable segments which are typically placed in closures and encapsulated are the area where two or more cables are spliced together (i.e., a splice), the end of the cable (i.e., an end block), and the junction between an air pressurized cable and a hydrocarbon grease filled cable (i.e., pressure block).
In addition to preventing water migration into the telecommunication cable splice, it is often desirable for the encapsulant to be re-enterable. Re-enterable means that upon opening a closure containing a cured encapsulant, the encapsulant can be entirely removed from the splice area by hand (using no tools in the area around the copper wires or fiber optic filaments) without damaging the individual wire or filament connections and without removing any of the insulation on the copper wires or any of the coating on the fiber optic filaments. Since the splice closure is encapsulated at on-site locations in the field where the cable is being layed, the encapsulant must also be capable of being poured as well as cured over a wide range of ambient temperatures (35.degree.-100.degree. F.).
Among the materials exhibiting insulation and thermal resistance properties which are desirable for encapsulation purposes are terpolymers of ethylene, propylene and a nonconjugated diene (i.e., "EPDM"). Thus, U.S. Pat. No. 3,974,132 to Valdiserri discloses the insulation and coating of electrically conducting wire with EPDM which is crosslinked with a trialkyl phosphate. However, several disadvantages are associated with the use of EPDM polymers such as those disclosed in this patent.
Primary among these disadvantages is that the EPDM employed in the Valdiserri and other similar processes is a high molecular weight material which must be pelletized. Consequently, in order to adapt the embedding composition to the configuration of the circuitry to be protected, such pelletized EPDM must be simultaneously subjected to heat and pressure. Such pressure and temperature requirements prohibit the accomplishment of on-site encapsulation of telecommunication cables, e.g., for the protection of splices or other on-site repairs.
U.S. Pat. No. 3,448,174, issued to Loveless, shows low molecular weight epoxy-modified ethylene/propylene/dicyclopentadiene terpolymers wherein the pendent dicyclopentadiene group itself is epoxy modified, and discloses that such compounds are useful as casting and coating compositions.
Tachi et al, in U.S. Pat. No. 4,245,061, disclose epoxy-modified waxes having a number average molecular weight of between 600 and 10,000. Such waxes are blended with a thermosetting resin to form compositions which are useful as paints, adhesives or molding materials.
U.S. Pat. No. 4,388,202, issued to Nagano et al, discloses lubricating oil compositions which comprise uncured epoxy-grafted polymers having saturated backbones and number average molecular weights ranging from about 5,000 to about 100,000.
However, none of the above-discussed patents disclose an encapsulation composition for telecommunication cables which may be readily applied and cured at or near ambient temperatures and pressures, which would not endanger the wires or filaments to be protected and which is amenable to on-site application to protect splices and the like.
Accordingly, it is an object of this invention to provide a pourable liquid encapsulation composition which may be cured at ambient or slightly elevated temperatures and pressures, and which may therefore be employed to protect metallic and/or fiber optic telecommunication cables.
It is further object of this invention to provide an encapsulation composition which may be employed for on-site applications.
It is yet another object of this invention to provide a method of encapsulating telecommunications cables employing such composition.
It is yet another object of this invention to provide an epoxy-grafted polymer which may be employed in the composition of this invention.
It is yet a further object of this invention to provide a telecommunications cable segment encapsulated with such an encapsulant composition.
The above objects and additional objects will become more fully apparent from the following description and accompanying Examples.